Custom fields
Custom fields allow you to add additional information to several types of data used in Redmine.
Read more information about Redmine Custom fields on Redmine Administration Guide: Redmine Custom fields
Redmine API (Application Programm Interface) partially supports the Custom Fields.
Using custom fields allows you to add specific hour start/end time slots to your Outlook calendar by using Start/End Time custom fields.
How to set specific hour in the Redmine ticket in Outlook: Start/End Time in hh:mm
To use it you need to install the Redmine Shared Api plugin:
https://github.com/ANovitsky/redmine_shared_api
Contact your Redmine admin for the installation. Then custom fields will work in the Outlook Add-in.